1. Field of the Invention
The present invention relates to a cathode ray tube and, more particularly, to a mask-frame assembly that can solve problems caused by a doming of a shadow mask of the cathode ray tube.
2. Description of the Related Art
Generally, a cathode ray tube is a display device that can display an image by the landing of electron beams, emitted from an electron gun, on phosphors formed on a face panel through a shadow mask.
The shadow mask is suspended inside the face panel by a mask frame. A mask-frame assembly is classified into two types depending on welding position of the shadow mask on the mask frame: a MIFA type and a MOFA type.
In the MIFA type, the shadow mask is welded on an outer surface of the mask frame, while in the MOFA type, the shadow mask is welded on an inner surface of the mask frame.
FIG. 3 shows a conventional mask-frame assembly.
A mask frame 2 comprises a front portion 6 which has an opening through which electron beams pass and a side portion 8, normal to the plane of the front portion 6, at the periphery of the front portion 6.
A shadow mask 10 can be welded on the inner or outer surface of the side portion 8 of the mask frame 2 as mentioned above.
The shadow mask 10 comprises a front screen portion 14 on which a plurality of electron beam converging apertures 12 are formed and a skirt portion 16 perpendicularly extending from the front screen portion 14. The curvature of a front screen portion is the same as the inner curvature of a face panel.
In the above described conventional mask frame assembly, it is well known that 15-18% of the electron beams pass through the apertures 12 of the shadow mask 10, while 82-85% strike the surface of the shadow mask 10.
The striking of the electron beams on the shadow mask 10 causes the shadow mask to be heated. As a result, doming of the shadow mask occurs, deteriorating color purity and white characteristics. Accordingly, the mask frame has been designed to compensate for the doming of a shadow mask.
However, this can not sufficiently solve the problems caused by doming. Particularly, when the mask-frame assembly is designed in the MIFA type, since the side portion of the mask frame restricts the thermal expansion of the skirt portion of the shadow mask, the problems caused by doming are worse.
Furthermore, in case of the large-screen cathode ray tube, i.e., more than 25 inches diagonally, deterioration of display quality caused by doming is more serious.
The present invention has been made in an effort to solve the above problems.
It is an objective of the present invention to provide a mask frame assembly that can improve display quality of a cathode ray tube by rapidly transmitting heat throughout a shadow mask.
To achieve the above objective, the present invention provides a mask-frame assembly for a cathode ray tube comprising a mask frame having a front portion and a side portion perpendicularly extending from the edge of the front portion and having notches, and a shadow mask having a front screen portion and a skirt portion welded to non-notched parts of the side portion of the mask frame.
The skirt portion of the shadow mask has indents at locations corresponding to the non-notched parts of the mask frame.